Takumi is Corrin's younger brother. When Rinkah and Kaze return Corrin to Hoshido, Takumi makes it very clear that he does not trust them, and believes them to be spying on them for Nohr. After Mikoto's assassination, Takumi blames Corrin for bringing the blade that killed her to Hoshido.

Takumi is wary of others, and quick to be suspicious. Although he is slow to open up, he is extremely loyal to his close friends. Takumi handles betrayal very poorly, and constantly calls Nohr-aligned Corrin a traitor to their face. Takumi also has severe self-esteem issues; he compulsively compares himself to his siblings and son, and has expressed the belief that his siblings do not care about his well-being on at least two separate occasions.

Throughout Conquest, his sanity continuously degrades as a result of his possession, and by the end of the game he has been reduced to a husk of his former self, completely obsessed with murdering Corrin and all Nohrians to exact revenge for their betrayal. Heroes expands upon his personality in this state; he typically cycles through episodes of confusion and bloodlust, but consistently displays his hatred towards Nohr. When Corrin, on the brink of death, encounters Takumi's sane spirit, however, Takumi is willing to reconcile with them and trust them to save him and restore peace to the world.

Voice Sample:
https://www.youtube.com/watch?v=C_xukD5rwok